public class ImplementStrstr {

    public static void main(String[] args) {
        System.out.println(strStr2("qweasdfa", "sdf"));
    }

    public static int strStr(String haystack, String needle) {
        return haystack.indexOf(needle);
    }

    public static int strStr2(String haystack, String needle) {
        int nLength = needle.length();
        if (nLength == 0) {
            return 0;
        }
        for(int left=0, right=nLength-1;right < haystack.length();left++, right++) {
            int i=left;
            for (int nIndex=0;i <= right;i++,nIndex++) {
                if (haystack.charAt(i) != needle.charAt(nIndex)) {
                    break;
                }
            }
            if (i==right+1) return left;
        }
        return -1;
    }
}
